GW Deep Percolation
These methods are used to model vertical losses from groundwater storage to a deeper, underlying aquifer.
NoneThis is the default method. It performs no calculations.
There are no slots specific to this method.
Input PercolationThis method is used if you want to input the amount of vertical loss or percolation. This method is dependent on the selection of the Single Computed Outflow in the Solution Type category.
Slots Specific to This Method
Percolation
Type: SeriesSlot
Units: FLOW
Description: the flow rate of water lost vertically to deeper groundwater storage
Information:
I/O: Optional; if not input it is set to zero.
Links: May be linked to the Inflow slot on a Groundwater Storage object.
Method Details
A local variable, storage flow, is calculated as the previous timestep’s Storage value divided by the length of the current timestep. This represents the flow rate required to drain the aquifer of all its stored water in the current timestep. If the input value of Percolation is greater than storage flow, an error is posted and the run terminates. Otherwise, Percolation is converted to a volumetric value and is included in the mass balance (see “Dispatch Methods”).
Linear PercolationThis method calculates Percolation in the same way Outflow is calculated by the Linear Flow method in the Groundwater Outflow category. This method is dependent upon the selection of the Single Computed Outflow in the Solution Type category.
Slots Specific to This Method
Percolation
Type: SeriesSlot
Units: FLOW
Description: the flow rate of water lost vertically to deeper groundwater storage
Information:
I/O: Output only
Links: May be linked to the Inflow slot on a Groundwater Storage object.
Percolation Alpha Param
Type: TableSlot
Units: PER TIME
Description: an empirical parameter used in the equation to calculate Percolation
Information:
I/O: Required input
Links: Not linkable
Method Details
Percolation is calculated as follows:
Exponential PercolationThis method calculates Percolation in the same way Outflow is calculated by the ExponentialFlow method in the Groundwater Outflow category. This method is dependent upon the selection of the Single Computed Outflow in the Solution Type Category.
Note: This calculation is carried out in user units. The value set in the Percolation Beta Param slot, as set by the user, must be consistent with the user units for the Storage slot. Changing the user units on the Storage slot will produce a different result; there will not be an automatic conversion of the Percolation Beta Param value.
Slots Specific to This Method
Percolation
Type: SeriesSlot
Units: FLOW
Description: the flow rate of water lost vertically to deeper groundwater storage
Information:
I/O: Output only
Links: May be linked to the Inflow slot on a Groundwater Storage object.
Percolation Alpha Param
Type: TableSlot
Units: PER TIME
Description: an empirical parameter used in the equation to calculate Percolation
Information:
I/O: Required input
Links: Not linkable
Percolation Beta Param
Type: TableSlot
Units: NONE
Description: an empirical parameter in the equation to calculate Percolation
Information: This value must be consistent with the user units for the Storage slot. If the user units on the Storage slot are changed, the value in this slot must be changed manually to correspond to the new units; otherwise, different results will be produced.
I/O: Required input
Links: Not linkable
Method Details
Percolation is calculated by the empirical equation:
The exponential term is computed in user units. That is, Storage(t‑1) is converted to user units, raised to the power of Percolation Beta Param, and then converted back to the standard RiverWare units before being multiplied by Percolation Alpha Param).
Head Based PercolationThis method is dependent upon the selection of the Head Based Groundwater Grid or the Link to MODFLOW GW in the Solution Type category. This method is used to calculate vertical flow to a deeper aquifer or to incorporate boundary conditions.
Slots Specific to This Method
Percolation
Type: Series Slot
Units: flow
Description: The flow to the deep aquifer
Information: Computed based on the previous timestep elevation difference. A positive value represents an outflow to the deep aquifer.
I/O: Typically output, but can be input or set by a rule.
Links: May be linked to another groundwater object
Deep Aquifer Conductance
Type: Scalar Slot
Units: area per time
Description: The conductance between the groundwater storage object and the deep aquifer
Information:
I/O: Input or computed; see “Groundwater Conductance”.
Links: Not linkable
Deep Aquifer Elevation
Type: Series Slot
Units: length
Description: The elevation/head associated with the deep aquifer. Datum should be consistent throughout all related objects’ elevation and stages slots.
Information: The previous timestep (beginning of timestep) value is used to compute Percolation
I/O: Required input
Links: Not linkable
Method Details
The Head Based Percolation method is called from the dispatch method. Percolation is computed as follows:
Note: The percolation cannot be larger than the previous Storage, converted to a flow. The computed Percolation value is passed back to the dispatch method and used in the mass balance equation to solve for the current Storage.
Head Based Linked PercolationThis method is dependent on the selection of the Head Based Groundwater Grid in the Solution Type category. This method is used to calculate vertical flow to a deeper aquifer or to incorporate boundary conditions. In this method, the deep aquifer elevation is linked to another object below it, usually an aquifer, “Specify or Link Flows”.
Slots Specific to This Method
Percolation
Type: Series Slot
Units: flow
Description: The flow to the deep aquifer
Information: Computed based on the previous timestep elevation difference. A positive value represents an outflow to the deep aquifer.
I/O: Typically output, but can be input or set by a rule.
Links: May be linked to another groundwater object
Deep Aquifer Conductance
Type: Scalar Slot
Units: area per time
Description: The conductance between the groundwater storage object and the deep aquifer
Information: This should be the same value as the object below
I/O: Input or computed; see “Groundwater Conductance”.
Links: Not linkable
Deep Aquifer Elevation Previous
Type: Series Slot
Units: length
Description: The elevation/head associated with the deep aquifer. Datum should be consistent throughout all related objects’ elevation and stages slots.
Information: This value is used to compute Percolation
I/O: Computed by linked object
Links: Linkable, often to the Head Previous on an Aquifer object below.
Method Details
The Head Based Percolation method is called from the dispatch method. Percolation is computed as follows:
The percolation cannot be larger than the previous Storage, converted to a flow. The computed Percolation value is passed back to the dispatch method and used in the mass balance equation to solve for the current Storage.
Revised: 11/11/2019